A Brazilian investigative reporter was found decapitated in southeastern Minas Gerais state as he followed leads in a drug-dealing and child prostitution case, a journalists' union told AFP Tuesday.

"The union is demanding a rigorous investigation. Independent journalist Evany Jose Metzker was warned he ran a risk investigating drug trafficking and child prostitution in this violent region," a union spokesman said.

The union denounced what it termed an attack on freedom and the right to inform.

Metzker, 67, had been working on a series of stories for three months in the Jequitinhonha Valley, one of Brazil's poorest regions.

The reporter had been missing for five days before his bound and badly marked and decomposing body was found Monday, Extra daily quoted police as saying.

Extra quoted Metzker's family as saying an anonymous tip off had led police to the body.

An initial autopsy carried out in the nearby town of Teofilo Otoni was unable to establish the cause of death and the body was transferred to state capital Belo Horizonte for further tests.